A continuous distribution of sound energy, referred to as an “acoustic field”, may be used for a range of applications including haptic feedback in mid-air, parametric audio and the levitation of objects.
By defining one or more control points in space, the acoustic field can be controlled. Each point can be assigned a value equating to a desired amplitude at the control point. A physical set of transducers can then be controlled to create an acoustic field exhibiting the desired amplitude at the control points.
For this control to be effective there must be as many transducers as possible in order to create enough degrees of freedom for the acoustic field to asymptotically approach the desired configuration. However, from a commercial perspective, using individually actuated transducers is an expensive solution, prone to transducer element failure and variability. From this perspective, reducing the number of elements is preferred, leading to reductions in acoustic capabilities. Being able to reduce the number and complexity of the electrically actuated components, while being able to retain acoustic versatility, is therefore advantageous.
One set of solutions to achieve these goals is the use of metamaterial, which is a material that has artificially designed structural properties that change its physical behavior in ways that may be generally unavailable in existing materials. Metamaterials are used to control and manipulate light, sound, and many other physical phenomena. The properties of metamaterials are derived both from the inherent properties of their constituent materials and from the geometrical arrangement of those materials.
Furthermore, to create haptic feedback, an array of transducers is actuated to produce an ultrasonic acoustic field that then induces a haptic effect. It has been discovered through simulations and testing that for best effect the transducers must be positioned in non-uniform or irregular patterns. While this can be to some extent achieved for positioning during printed circuit board (PCB) assembly, arbitrary positioning raises the cost of the assembly process and reduces the transducer density possible. If there is a method to achieve this positioning of acoustic sources without resorting to complex and costly assembly processes, then there is a commercial advantage in such a method. By producing the metamaterial such that an irregular pattern is expressed, this can be achieved without requiring this extra assembly cost.
Furthermore, by focusing at a point, acoustic waves with increased power are created and can be used to generate a constant force. The force generated is small but naturally non-contact. Further applications of the non-contact forces may also lead to commercially viable devices.
Current designed metamaterials generally incorporate only static structure. By including structures that can be dynamically switched between states through time, the properties of the metamaterial can be modified on the fly. These changes can be affected such that the metamaterial and transducer system can behave as though the input signal has changed, without actually changing the input signal. This is equivalent to effectively modifying the acoustic wave after, rather than before, leaving the transducer element.
This allows for a further division of labor and the resultant efficiency and potential cost savings. This is achieved by using a single or few highly efficient and powerful sources to generate a (generally monochromatic) acoustic wave that is then modified by switching metamaterial elements which are integrated into the material. This behaves similarly to the a transducer array. In this way, together the acoustic source and each element of the metamaterial may work together as a transducing element, only now the waveform modifications are expressed by the actable metamaterial layer.
Accordingly, it is desirable to implement one or more of the above techniques to achieve the goal of more effective and efficient use of transducers in haptic systems.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.